The present invention relates to a method and a device for cleaning objects, preferably spray guns, whereby washing liquid is discharged by at least one washing-liquid nozzle for cleaning the object and whereby at least one pressure-medium operated, preferably compressed-air operated, washing-liquid pump is actuated for generating a pulsating flow of washing liquid in a washing-liquid conduit which is provided between said pump and said nozzle.
A prior art cleaning method for cleaning spray guns is described in EP 0 300 248. In this prior art method however, there are some drawbacks because the washing time is normally determined by pneumatic or mechanical timers. The timer starts to meter the washing time independent of if and how much washing liquid there is in the washing-liquid conduit between the washing-liquid pump and the nozzle. If e.g. said conduit is completely filled with washing liquid, washing begins immediately when the timer starts the washing-liquid pump. If however, the washing liquid conduit is not filled with washing liquid, it takes a certain time before washing begins, namely the time it takes for the washing-liquid pump to fill the washing-liquid conduit.
For the above reasons, the washing time desired by the timer and the actual washing time will not correspond, but the actual washing time will vary substantially depending on how much washing liquid there is in the washing-liquid conduit. This is not acceptable since the actual washing time thereby might be much too short for an acceptable cleaning of the spray gun.
Said difference between the desired and the actual washing time can e.g. be particularly troublesome at short washing times, e.g. during rinsing of the spray gun with clean washing liquid after having washed the spray gun with washing liquid that is recirculated. During such rinsing a short washing time is normally selected for saving pure washing liquid, inter alia because pure washing liquid is available only in limited amounts.
If the liquid conduit during this short-time rinsing of the spray gun initially is empty, then the actual washing time can only be half as long as the desired washing time, which thus might lead to a faulty cleaning of the spray gun.
An example of acceptable consumption of pure washing liquid during rinsing is in the order of 3 dl. A typical stroke volume for a washing-liquid pump often used for cleaning purposes is about 1 dl and a typical example of the frequency of such a pump is 1 stroke per second (1 Hz).
Consequently, a timer for the abovementioned rinsing should be set for 3 seconds of rinsing. It is however difficult to manufacture a pneumatic or mechnical timer with such a precision or accuracy. If e.g. the timer has a tolerance of xc2x12 seconds, this will give a variation in the washing-liquid consumption of xc2x12 dl, i.e. the consumption of washing liquid varies between 1 and 5 dl, which means an uncontrolled consumption and an uncontrolled or inaccurate washing result.
The inaccuracy with a filled or not filled washing-liquid conduit together with an inaccurate timer might thus result in a completely erroneous washing result, particularly during short time washing cycles, since the desired and actual washing-liquid amounts during each cycle will not correspond.
The object of the present invention has been to eliminate the abovementioned problem and this is arrived at by means of the method of the present invention.
Said problem is also eliminated by means of the device of the present invention.
By counting the number of pulses of the pulsating flow of washing liquid in the washing-liquid conduit and by breaking or interrupting the operation of the washing-liquid pump in dependence of a predetermined number of pulses, it is ensured that the desired and the actually discharged amount of washing liquid during each washing process are the same.